The difficulties in monitoring fetal well-being have long been recognized by the medical profession. The position of the fetus within the womb, surrounded by the amnion and amniotic fluid makes direct examination of the fetus impossible or very difficult using most examination techniques.
Traditional methods for examination of fetuses have included using a stethoscope to listen to the fetal heartbeat, and physical examination by palpatation of the female anatomy surrounding the fetus. Although these techniques are useful they are limited in the amount of information derived. They are also performed during relatively short periods of time during a visit to the physician's office. Accordingly, they do not provide sufficient information concerning the health of the fetus in response to varying environmental conditions and unexpected occurrences confronting the mother and fetus.
Other techniques for determining fetal conditions include the use of ultrasound. The ultrasound techniques generally use an apparatus which includes an ultrasonic transducer which generates ultrasonic vibrations which are directed at the fetal heart or other organs. Ultrasonic waves reflect off of the anatomical parts of the fetus and are sensed by an appropriate sensor and processed to determine the frequency shift associated with reflection from the moving fetal heart valve according to the well-known Doppler Principle. The information gained by such techniques is then analyzed and integrated to provide information about the fetus, including fetal heart rate. Such testing equipment is costly and is usually used by hospitals and other public health facilities. The high cost also limits the amount of time any one fetus can be monitored. Such equipment is also relatively large and bulky and has not been developed into a portable system which can be used to monitor fetal well-being while the mother functions in her normal life. Accordingly, such nonambulatory equipment has not been satisfactory for use in medical studies seeking to determine effects on the fetus of various environmental and behavioral factors, and health patterns experienced or practiced by the mother.
Ultrasound techniques for determining fetal heart rate are also disadvantageous because they are invasive in nature, applying a stream of high frequency ultrasonic vibration to the developing fetus and fetal heart valve. Such invasive properties may have significant detrimental effects on the fetus. They further require a relatively tedious alignment of the ultrasonic transducer with the fetal heart. Even moderate movement of the patient often results in erroneous readings and increased examination time and costs.
Prior art includes several types of fetal monitors. An early fetal heart monitor is described in U.S. Pat. No. 2,536,527 to Appel. The Appel invention was designed for monitoring fetal condition during delivery. A microphone communicates with a stethoscope to produce a signal which is amplified, filtered, rectified and used to control two relays which indicate abnormally high or low heart rates or amplitudes of the fetal heart.
U.S. Pat. No. 3,187,098 to Farrar et al discloses a fetal heartbeat detector. The Farrar detector uses a cantilevered piezoelectric crystal mounted within a contacting slab so as to have a natural frequency of approximately greater than 50 Hz.
Another fetal monitor is shown in U.S. Pat. No. 3,409,737 to Settler et al. The Settler monitor is used with a belt having three spaced microphones. A three stage amplification circuit is used to selectively amplify the fetal heartbeat and remove the maternal heartbeat.
U.S. Pat. No. 3,599,628 to Abbenante et al discloses a device for monitoring fetal heartbeat and intrauterine pressure for the purpose of correlating these two parameters and indicating fetal distress therefrom. A catheter is inserted into the uterus and is liquid coupled to a piezoelectric pressure transducer to determine the intrauterine pressure. A probe is attached directly to the fetus to measure the fetal ECG. Such a system is only practical for use during delivery.
U.S. Pat. No. 3,703,168 discloses a fetal heart monitor having electrodes which are positioned against the skin of the mother to derive an electrical signal therefrom. A fetal ECG is derived from the electrode signal as is a signal indicative of maternal contractions.
A further fetal monitor used to detect intrauterine contractions and fetal heart rate is described in U.S. Pat. No. 3,989,034. An indication of fetal distress is derived therefrom.
Sureau et al discloses a fetal heart rate apparatus useful during labor to measure the decelerations in fetal heart rate during uterine contractions (U.S. Pat. No. 4,027,057).
U.S. Pat. No. 4,299,234 to Epstein et al discloses a fetal heart rate monitor which combines electrocardiogram and electromyogram types signals to increase the reliability and accuracy of the resulting heart rate information.
Prior art fetal monitors have been limited in their usefulness because of their typical sole function of analyzing an input signal to determine fetal heart rate. Some have also utilized the intrauterine pressure parameter as a further indicator fetal stress. However, none are designed to provide an ambulatory monitor which can continuously and automatically analyze fetal well-being using more complex analyses based upon heart rate patterns and movements of the fetus.
Absence of such an ambulatory fetal monitor from the prior art has made it impossible to effectively monitor and warn the mother of many health risks to the fetus, such as caused by maternal activities such as smoking, drinking or drug consumption. Any current testing directed to these problems must be done in a clinical setting which does little or nothing to help the large number of untested mothers to recognize the problem and is of depreciated scientific value because of the differences in consumption patterns and activity as compared to the patients normal lifestyle. Such clinical testing is also limited since more subtle variations in lifestyle can also not be explored as significant factors to determine the effects on fetal well-being.
In addition to the recognized risks associated with alcohol, tobacco and drug consumption, there are additional environmental factors and activities which may have a discernible effect on fetal well-being. Investigation of such factors as exposure to industrial, agricultural and laboratory chemicals may be of particular importance. Toxic chemical exposure in the home may be of even greater importance. High levels of activity such as running, cycling, aerobics and hiking may also have discernible effects on the fetus, but cannot currently be effectively tested. The effect of stressful situations and maternal emotional traumas upon fetal well-being may also be investigated with a continuous ambulatory fetal monitor whereas prior art clinical monitors cannot be effectively used. The effects on the fetus of maternal infections from viral and bacterial pathogens may also be investigated in an accurate and reliable manner when continuous monitoring during routine life is made possible.
A continuous ambulatory fetal monitor is also advantageous for use with mothers having a higher risk of pregnancy-related complications. Such an ambulatory monitor can provide additional peace of mind not otherwise available for such patients, and can potentially mean the difference between life and death in critical circumstances.